1. Field of the Invention
The present invention relates to a pneumatic tire. In particularly, the present invention relates to a pneumatic tire having a lug pattern capable of improving a heat radiation effect of a tread used for a heavily loaded vehicle.
2. Description of the Related Art
Conventionally, a tread rubber with a good wear resistance has been used in order to ensure improvement of wear resistance of an pneumatic tire (hereinafter, referred to as a tire, for convenience). In addition, in a tread as well, there has been used a method in which a tread volume is increased, a tread gauge is thickened, and a negative ratio in tread is lowered.
In the meantime, recently, an increase of tire size, low aspect ratio trend of the tire, and heavy loading on the tire of a construction vehicle is accelerated due to the increase in size thereof in order to achieve a higher productivity. Moreover, a construction vehicle with a higher speed is also being widely developed. Under such a circumference, heat generation of a tread portion is increased due to a higher speed of the (heavy) vehicle, which may cause troubles such as heat separation of the tread portion.
That is, heat generation of the tire tread portion is caused by repetition of a tread compression stress experienced in a tire grounding region and a bending stress generated at a stepping-in portion and a kicking-outportion. In particular, in a heavily loaded tire for an off-the-road in which the tread gauge thickness is relatively thick, the tread volume at the tire center portion is increased, and thus heat buildup therein is also increased. As a result, the temperature at the center portion increases during vehicle running, which may cause a heat separation trouble.
The present invention has been made in consideration of the above facts. It is an object of the present invention-to provide an pneumatic tire capable of reducing the wear of a tread to the minimum, and improving a heat radiation effect.
According to a first aspect of the present invention, there is provided an pneumatic tire comprising: a tread; a lug groove extending from a shoulder side of said tread toward a tire central (equatorial) plane, the lug groove being provided in plurality at said tread in the tire peripheral direction to form a lug pattern; and a recess portion being provided in a center region of the tread, the center region extending in the tire peripheral direction with a width that in 50% of a maximum width (w) of tire ground contacting portion so as to be symmetrical with respect to the tire central plane of said tread, wherein a negative ratio of the center region other than said lug groove is set to 10% to 25% and an axially inner groove edge of each lug groove is aligned on the central plane.
According to this aspect, the negative ratio of the center region is set within the above range, whereby the improvement of heat generation properties (more precisely, generated-heat-radiation properties, which will be referred to as xe2x80x9cheat radiation propertiesxe2x80x9d hereinafter) and the reduction of wear can be made compatible with each other.
According to a second aspect of the present invention, the depth of a recess portion of the above pneumatic tire is 10% to 45% of the maximum depth of the lug groove.
According to this aspect, the depth of the recess portion is set to 10% to 45% of the maximum depth of the lug groove. Thus, heat radiation properties of the tread is improved, and the wear of the tread can be reduced.
According to a third aspect of the present invention, a recess portion of the pneumatic is an auxiliary groove sequentially formed in the circumferential direction of the tire.
According to this aspect, the recess portion is provided as an auxiliary groove sequentially formed in the circumferential direction of the tire, whereby an air flow can be improved during tire rolling. Thus, heat radiation properties of the tire can be improved.
According to a fourth aspect of the present invention, the depth of a lug groove of the above pneumatic tire is made gradually shallower from the shoulder side toward the tire central plane.
According to this aspect, the depth of the lug groove is made gradually shallower from the shoulder side toward the tire central plane, whereby the distribution of the tread rigidity can be uniformed, and the wear of the tread can be decreased.
According to a fifth aspect of the present invention, in the above pneumatic tire, the maximum depth of a lug groove in the center region that corresponds to 50% of the maximum width of tire ground contacting portion is 60 mm or more.
According to this aspect, in particular, in a relatively large tire of 24.00R49 or more in size, the maximum depth of the lug groove in the center region that corresponds to 50% of the maximum width of tire ground contacting portion sets 60 mm or more, and heat radiation properties of the tire can be effectively improved in spite of the increase in the tread volume and the heat generation.